Yep, it’s not the ones that came over you have to worry about, it’s their offspring that are citizens and become radicalized. This is going to be Europe’s real big problem in the future.
This phenomenon invalidates any useful attempt at vetting.
It may become a bigger problem in the future but I’d say it has already reached big problem status already.
They don’t “become” radicalized. They are raised in Islam and its all in the Islamic Operating Manual.